What we know so far about the deadly pager explosions in Lebanon and Syria

NEW YORK (AP) — In what appears to be a sophisticated, remote attack, pagers used by hundreds of members of Hezbollah exploded almost simultaneously in Lebanon and Syria Tuesday, killing at least nine people — including a young girl — and wounding thousands more.
The Iran-backed militant group blamed Israel for the deadly explosions, which targeted an extraordinary breadth of people and showed signs of being a long-planned operation. How the attack was executed is largely uncertain and investigators have not immediately said how the pagers were detonated. The Israeli military has declined to comment.
Here’s what we know so far.
Hezbollah leader Hassan Nasrallah previously warned the group’s members not to carry cellphones, saying they could be used by Israel to track the group’s movements for targeted strikes. As a result, the organization uses pagers to communicate.
READ MORE: Hezbollah members among hundreds wounded after pagers explode across Lebanon and Syria, officials say
A Hezbollah official told The Associated Press the exploded devices were from a new brand the group had not used before. The official, who spoke on condition of anonymity because he was not authorized to talk to the press, did not identify the brand name or supplier.
With little disclosed from investigators so far, multiple theories have emerged Tuesday around how the attack might have been carried out. Several experts who spoke with The Associated Press suggest that the explosions were likely the result of supply-chain interference.
Very small explosive devices may have been built into the pagers prior to their delivery to Hezbollah, and then all remotely triggered simultaneously, possibly with a radio signal, said Carlos Perez, director of security intelligence at TrustedSec. By the time of the attack, “more than likely the battery was probably half-explosive and half-actual battery.”
After security camera footage appeared on social media Tuesday purporting to show one of the pagers explode on a man’s hip in a Lebanese market, two munitions experts also said that the blast appeared to be the result of a tiny explosive device.
“Looking at the video, the size of the detonation is similar to that caused by an electric detonator alone or one that incorporates an extremely small, high-explosive charge,” said Sean Moorhouse, a former British Army officer and explosive ordinance disposal expert. He estimated the amount of explosive required could be as little as 1.5 grams to 2 grams — roughly the size of an eraser on the end of a pencil.
Moorhouse explains that the tiny explosives and the method for detonating them would have had to have been built into the pagers prior to delivery, signaling the likely involvement of a state actor. He adds that Israel’s foreign intelligence agency, the Mossad, is the most obvious suspect to have the resources to carry out such an attack.
N.R. Jenzen-Jones, an expert in military arms who is director of the Australian-based Armament Research Services, agreed that the scale and sophistication of the attack “almost certainly points to a state actor,” and that Israel had been accused of carrying out such operations in the past. Last year, AP reported that Iran accused Israel of trying to sabotage its ballistic missile program through faulty foreign parts that could explode, damaging or destroying the weapons before they could be used.
Another possibility is that malware could have been inserted into the operating system of the pagers — and that somehow caused the device batteries to all overload at a specific time, causing them to burst into flame.
According to a Hezbollah official and Lebanese security officials, the pagers first heated up and then exploded in the pockets, or the hands, of those carrying them Tuesday afternoon.
These pagers run on lithium ion batteries, the Hezboolah official said, claiming the devices exploded as the result of being targeted from an Israeli “security operation,” without elaborating further.
When overheated, lithium ion batteries can smoke, melt and even catch on fire. Rechargeable lithium batteries are used in consumer products ranging from cellphones and laptops to electric cars. Lithium battery fires can burn up to 590 C (1,100 F).
Still, Moorhouse and others noted that images and video footage seen Tuesday more strongly resembled the detonation of small explosive charge, not an overheating battery.
“A lithium ion battery fire is one thing, but I’ve never seen one explode like that. It looks like a small explosive charge,” Alex Plitsas, a weapons expert at the Atlantic Council.
Another possibility is an electronic pulse “that was sent from afar and burned the devices and caused their explosion,” said Yehoshua Kalisky, a scientist and senior researcher at the Institute for National Security Studies, a Tel Aviv think tank.
“It is not some random action; it was deliberate and known,” Kalisky added.